A method for preparing an Al-doped p-type silicon carbide powder

Abstract

The application discloses a preparation method of Al-doped p-type silicon carbide powder, which separates a first heating device and a second heating device by utilizing a hollow pipeline, reduces temperature crosstalk as much as possible, realizes decoupling heat treatment of carbon powder and silicon powder and an Al source, can control the release speed of the carbon powder and the silicon powder at the same time, controls the formation speed of silicon carbide, controls the release speed of the Al source, makes the Al source uniformly distributed and doped into the silicon carbide, avoids that the Al source is released too fast and overflows before reaction or is unevenly doped, that is, part of the silicon carbide is doped with more Al, and part of the silicon carbide is doped with less Al. In addition, a porous graphite sheet is arranged at the bottom of the first heating device, which can prevent the silicon liquid from leaking out, and make the Al source vapor smoothly pass into the first cavity and be uniformly doped into the silicon carbide.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material preparation technology, and particularly relates to a method for preparing Al-doped p-type silicon carbide powder. Background Technology

[0002] Silicon carbide (SiC) is one of the core representatives of third-generation semiconductor materials, with p-type conductive SiC being an indispensable material for manufacturing power devices. Doping SiC with aluminum (Al), the acceptor impurity, is the main technical approach for obtaining p-type SiC. Compared to traditional synthesis methods, growing p-type SiC single crystals using highly doped p-type SiC powder is one of the more effective methods for obtaining low resistivity crystals. This is because in traditional synthesis methods, the aluminum source (such as Al₄C₃), Si powder, and C powder are in the same high-temperature reaction zone. Due to its high vapor pressure, the aluminum source is easily consumed prematurely before the SiC matrix is ​​largely formed, resulting in a low and uneven overall aluminum doping concentration in the final synthesized powder, which is insufficient to meet the requirements for high-quality p-type single crystal growth. Therefore, developing a method for preparing p-type SiC powder with high Al doping efficiency and a large Al doping concentration is of great significance.

[0003] Patent application CN116240632A discloses a heavily doped p-type SiC single crystal, its growth method, and its applications. This invention utilizes compounds or solid solutions composed of aluminum and nitrogen as a primary doping source and other p-type doping sources as secondary doping sources for Al-N co-doping. Furthermore, AlN material is placed in the SiC powder region as a primary doping source, providing an equal molar ratio of Al and N atoms upon decomposition, thereby achieving synchronous release of the N and Al sources and maintaining the monomorphism of the heavily doped crystal. Al4C3, Al2O3, and Al are placed as secondary doping sources to provide additional Al elements, ensuring that the n[Al]:n[N] ratio is within the range of 1.2 to 3.0, guaranteeing that the grown crystal is a monomorphic p-type SiC. However, the apparatus provided in this patent application cannot use Si powder and C powder as raw materials to synthesize SiC, nor can it simultaneously control the Al source infiltration rate.

[0004] Patent application CN116145243A discloses a crucible and method for growing p-type SiC single crystals. The crucible includes an upper crucible, a lower crucible, and a connecting rod. The connecting rod is hollow, with one end connected to the lower opening of the upper crucible and the other end connected to the upper opening of the lower crucible. An inner crucible is located in the lower part of the upper crucible, with its opening facing upwards. The height of the inner crucible's sidewall is less than that of the upper crucible's sidewall. The space inside the inner crucible is a SiC powder placement area, and the space above the inner crucible in the upper crucible is a SiC single crystal growth area. A gap is formed between the inner and upper crucibles, and the lower opening of the upper crucible communicates with the SiC single crystal growth area through this gap. The upper lid of the upper crucible is designed to allow protective gas to enter the upper crucible from the lid. This invention effectively reduces the temperature of the dopant source, allowing for slow release of the dopant source and improving the uniformity of dopant source release. It effectively solves the problem of unstable crystal structure and quality deterioration caused by concentrated release of the dopant source. However, this patent application uses pre-synthesized SiC powder as raw material and does not involve the liquid phase.

[0005] While existing technologies in crystal growth (PVT) utilize dual-crucible structures to address doping unevenness, directly adapting such crystal growth equipment for powder synthesis presents significant technical hurdles. Crystal growth typically uses pre-synthesized SiC powder as raw material, avoiding the liquid phase; however, powder synthesis requires Si and C powders. During the high-temperature reaction, the Si powder melts first (melting point 1414 °C) to form liquid silicon. If a traditional interconnected dual-crucible structure is used directly, the molten liquid silicon and the mixed C powder will flow into the connecting pipes under gravity, causing blockages or even damaging the crucible containing the aluminum source below, leading to synthesis failure.

[0006] Therefore, there is an urgent need for a specific synthesis device and method that can achieve decoupled control of aluminum source release in both temperature zones and adapt to the characteristics of Si powder synthesis process (effective control of liquid-phase silicon). Summary of the Invention

[0007] This invention provides a method for preparing Al-doped p-type silicon carbide powder, which enables the Al source to be uniformly incorporated into the silicon carbide.

[0008] This invention provides a method for preparing Al-doped p-type silicon carbide powder, comprising: placing an Al-doped p-type α-SiC powder synthesis device into an induction heating furnace, sealing it, evacuating it, and filling it with argon gas until the pressure inside the furnace reaches 20~100mbar; The first chamber is heated to 2300-2500 ℃ by the first heating element, so that the carbon powder and silicon powder react to form silicon carbide. The second chamber is heated to 1500-1800 ℃ by the second heating element and kept at this temperature for 4-8 hours, so that the aluminum source enters the first addition device in the form of aluminum vapor through the central control pipe and is incorporated into SiC to obtain Al-doped p-type α-SiC powder. The Al-doped p-type α-SiC powder synthesis apparatus includes: The first heating device includes a first cavity and a first heating element surrounding the first cavity. A porous graphite sheet is placed at the bottom of the first cavity, and carbon powder and silicon powder are placed on the porous graphite sheet. A hollow pipe, which is connected to the bottom of the first cavity; The second heating device has its top connected to the bottom of the hollow pipe. The second heating device includes a second cavity and a second heating element surrounding the second cavity. An aluminum source is placed at the bottom of the second cavity.

[0009] This invention utilizes a hollow pipe to separate the first heating device and the second heating device, minimizing temperature crosstalk and achieving decoupled heat treatment of carbon powder and silicon powder from the Al source. It can simultaneously control the release rate of carbon powder and silicon powder, thereby controlling the formation rate of silicon carbide, and simultaneously control the release rate of the Al source, so that the Al source can be evenly distributed and incorporated into the interior of silicon carbide, avoiding the Al source being released too quickly and overflowing before it can react, or uneven incorporation, i.e., some parts of silicon carbide are incorporated in larger quantities and some parts in smaller quantities.

[0010] The present invention also provides a porous graphite sheet at the bottom of the first heating device, which can prevent silicon liquid from leaking out and allow Al source vapor to smoothly enter the first cavity and uniformly incorporate silicon carbide.

[0011] Preferably, the porous graphite sheet has a porosity of 40-60% and an average pore size of 20-60 μm.

[0012] This invention provides suitable porosity and average pore size, enabling porous graphite sheets to have good surface tension and physical support, thus keeping the molten liquid silicon and carbon powder mixture in the upper crucible for reaction and preventing the molten liquid silicon from dripping into the connecting pipe.

[0013] Preferably, the first heating element is a first high-frequency induction coil, and the power of the first high-frequency induction coil is set to 8000-10000 W, so that the temperature of the first cavity is 2300-2500 ℃. At this temperature, silicon powder melts and reacts with carbon powder to form SiC. Molten silicon quickly encapsulates and penetrates into the pores of carbon (C) powder particles, so that the generated SiC particles have high phase purity and crystal consistency. In the early stage of the reaction between liquid phase Si and solid phase C to form SiC lattice, aluminum vapor is more likely to replace silicon sites in the lattice, thereby achieving high concentration doping.

[0014] Preferably, the second heating element is a second high-frequency induction coil, and the power of the second high-frequency induction coil is set to 500-1500 W, so that the temperature of the first cavity is 1500-1800 ℃. At this temperature, the aluminum source is stably sublimated into aluminum vapor, and the aluminum vapor is controlled within a suitable flow rate range so that the aluminum element is uniformly doped into the SiC.

[0015] Preferably, the flow rate of the aluminum vapor is 0.06-0.08 m / s. This invention ensures a continuous and stable supply of aluminum source throughout the entire synthesis cycle by controlling the dual-temperature zone structure.

[0016] Preferably, the heat preservation process of the first and second cavities lasts for 4-8 hours. This invention, by controlling the heat preservation time, ensures complete in-situ reaction between carbon powder and molten silicon powder, and allows sufficient aluminum vapor source to be incorporated into the grown SiC lattice.

[0017] Preferably, the first cavity includes an upper isostatic graphite crucible and a sealed furnace cover located on the graphite crucible, the second cavity is a lower isostatic graphite crucible, and the hollow pipe is a hollow graphite pipe.

[0018] Preferably, carbon fiber insulation felt is wrapped between the first cavity and the first heating element, between the second cavity and the second heating element, and on the outside of the hollow pipe.

[0019] Preferably, the aluminum source is Al4C3.

[0020] Preferably, the length of the hollow pipe is 150-180 mm.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention addresses the characteristic of liquid silicon (Si melting point 1414 ℃) in the SiC powder synthesis process by introducing a porous graphite sheet structure into the upper crucible. This structure utilizes the surface tension and physical support of the porous medium to effectively prevent the molten silicon liquid at high temperature from carrying carbon powder and dripping into the hollow connecting pipe, thus avoiding pipe blockage and the interruption of the aluminum source channel. This successfully realizes the transformation of the double crucible structure from the field of "crystal growth" to the field of "powder synthesis".

[0022] (2) This invention uses a hollow pipe to form a double-cavity, double-heating-element group temperature-controlled thermal field structure, decoupling the SiC synthesis zone from the aluminum source supply zone in terms of space and temperature. By precisely controlling the crucible temperature within the range where the aluminum source can efficiently sublimate, and utilizing the temperature gradient to drive gas phase transport, a stable and sufficient supply of aluminum source is achieved throughout the powder preparation process. This results in synthesized p-type α-SiC powder with not only high crystal quality but also a significantly increased aluminum doping concentration. This invention has strong process controllability and good repeatability, providing crucial high-doped raw materials for the preparation of high-performance p-type SiC single crystals. Attached Figure Description

[0023] Figure 1 A schematic diagram of an Al-doped p-type α-SiC powder synthesis apparatus provided in a specific embodiment of the present invention; Figure 2 This is a temperature field diagram inside the crucible under steady state provided in Embodiment 1 of the present invention; Figure 3 This is a diagram showing the steady-state aluminum vapor velocity distribution inside a graphite pipe according to Embodiment 1 of the present invention. Figure 4 This is a flowchart illustrating a method for preparing Al-doped p-type α-SiC powder according to an embodiment of the present invention. Figure 5 This is a physical image of the Al-doped p-type α-SiC powder block provided in Embodiment 1 of the present invention; Figure 6 This is a physical image of the Al-doped p-type α-SiC powder obtained after crushing, as provided in Embodiment 1 of the present invention.

[0024] Figure 7 The image shows the XRD pattern of Al-doped p-type α-SiC powder provided in Example 1 of this invention.

[0025] Figure 8 The image shows the GDMS detection results of Al-doped p-type α-SiC powder provided in the embodiment of the present invention* (please provide).

[0026] 1-Coil; 1.1-First high-frequency induction coil; 1.2-Second high-frequency induction coil; 2-Quartz wall; 3-Carbon fiber insulation felt; 4-Argon gas; 5-Aluminum source; 6-Hollow graphite tube; 7-Porous graphite sheet; 8-Si powder, C powder; 9-Sealed furnace lid; 10-Graphite crucible; 10.1 Upper graphite crucible; 10.2 Lower graphite crucible. Detailed Implementation

[0027] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention... The invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0028] like Figure 1 As shown in the figure, a specific embodiment of the present invention provides an Al-doped p-type α-SiC powder synthesis device, including a first heating device, a hollow pipe, and a second heating device.

[0029] The first heating device provided in this embodiment of the invention includes a first cavity and a first heating element surrounding the first cavity. A porous graphite sheet is placed at the bottom of the first cavity, and carbon powder and silicon powder 8 are placed on the porous graphite sheet. The first heating element is used to heat the first cavity to 2300-2500 ℃, so that the carbon powder and silicon powder 8 react to form silicon carbide.

[0030] The first cavity is an upper graphite crucible 10.1 and a sealed furnace cover 9 located on the graphite crucible 10.1, and the first heating element surrounding the first cavity is a first high-frequency induction coil 1.1.

[0031] The hollow pipe provided in this embodiment of the invention is a hollow graphite pipe 6. The top of the second heating device provided in this embodiment of the invention is connected to the bottom of the hollow pipe. The second heating device includes a second cavity and a second heating element surrounding the second cavity. An aluminum source 5 is placed at the bottom of the second cavity. The second heating element is used to heat the first cavity to 1500-1800 ℃, so that the aluminum source enters the first addition device in the form of aluminum vapor through the central control pipe and is incorporated into SiC.

[0032] The second cavity is a lower graphite crucible 10.2, and the second heating element surrounding the second cavity is a second high-frequency induction coil 12.

[0033] In a specific embodiment of the present invention, carbon fiber insulation felt 3 is wrapped between the first cavity and the first heating element, between the second cavity and the second heating element, and on the outside of the hollow pipe.

[0034] In a specific embodiment of the present invention, a quartz wall 2 is provided between the carbon fiber thermal insulation felt 3 and the coil 1.

[0035] Example 1 This embodiment provides a method for preparing Al-doped p-type α-SiC powder, such as... Figure 4 As shown, the specific steps are as follows: S1: System Assembly and Loading: Two isostatic graphite crucibles of matching specifications, namely an upper isostatic graphite crucible and a lower isostatic graphite crucible, are connected by a hollow graphite pipe with an inner diameter of 25 mm. A high-purity porous graphite sheet with a thickness of 3-5 mm is placed at the bottom of the upper isostatic graphite crucible. In this embodiment, the selected porous graphite sheet has a porosity of 50% and an average pore size of 40 μm. This parameter is chosen to balance gas permeability and barrier properties to liquid silicon: too large a pore size (e.g., exceeding 100 μm) may cause liquid silicon to overcome surface tension and drip under gravity, while too low a porosity will hinder the transport of aluminum vapor below. High-purity Si powder (purity >99.999%) and high-purity carbon powder (purity >99.995%), precisely weighed in a 1:1 molar ratio, are loaded onto the porous graphite sheet in the upper crucible, with a total mass of 2000 g. 20g of high-purity Al4C3 powder (purity >99%) was placed into the crucible. Then, a 20mm thick layer of carbon fiber thermal insulation felt was uniformly wrapped around the outside of the assembly.

[0036] S2: Vacuuming and Atmosphere Control: Place the assembled system inside the induction heating furnace chamber and seal the furnace lid. Start the molecular pump assembly to evacuate the furnace chamber to a high vacuum. When the vacuum level reaches 5 × 10⁻⁶... ⁻5 After reaching 80 mbar, maintain this pressure for 30 minutes to ensure complete degassing of the system. Then, introduce high-purity argon into the furnace until the pressure stabilizes at 80 mbar.

[0037] S3: Dual-coil heating and synthesis: The independently controlled power supply is activated to power the first and second high-frequency induction coil groups. The power of the first (upper) high-frequency induction coil group increases to 9000 W at a relatively gradual rate (approximately 10 °C / min) and remains stable, corresponding to an upper zone temperature of approximately 2450 °C. The power of the second (lower) high-frequency induction coil group increases to 1000 W at a slower rate (approximately 5 °C / min) and remains stable, corresponding to a lower zone temperature of approximately 1600 °C. Under these conditions, the temperature is maintained for 5 hours.

[0038] S4: Cooling and Product Collection: After the preparation process is completed, all heating power is turned off, and the furnace is allowed to cool naturally to room temperature under an argon atmosphere (approximately 12 hours). The upper crucible is opened in a clean bench, and light gray to dark gray Al-doped α-SiC powder is collected.

[0039] Testing showed that the aluminum doping concentration in the powder obtained in this embodiment was uniform, with a doping concentration of 1.58 × 10⁻⁶. 20 cm -3 The quantity is sufficient to meet the raw material requirements for p-type SiC single crystal growth.

[0040] Example 2 This embodiment aims to explore the effect of increasing the aluminum source supply to further improve the doping concentration.

[0041] S1: System Assembly and Loading: This step is basically the same as in Example 1, except that the amount of Al4C3 powder loaded into the crucible is increased to 25g.

[0042] S2: Vacuuming and Atmosphere Control: This step is the same as in Example 1, involving evacuating to an absolute pressure of 5 × 10⁻⁶. ⁻5 mbar, then high-purity argon gas is introduced until the pressure stabilizes at 20~100 mbar.

[0043] S3: Dual-coil heating and synthesis: This step is basically the same as in Example 1, except for the adjustment of process parameters: the power of the first group (upper) coil is set to 9200 W (corresponding to an upper zone temperature of approximately 2080 ℃), and the power of the second group (lower) coil is set to 1100 W (corresponding to a lower zone temperature of approximately 1650 ℃). The heat preservation time is extended to 6.5 hours.

[0044] S4: Cooling and Product Collection: This step is the same as in Example 1.

[0045] Testing showed that the average aluminum doping concentration of the powder obtained in this embodiment was increased to 7.74 × 10⁻⁶. 19 cm -3 This result demonstrates that, by optimizing the aluminum source amount and appropriately increasing the crucible temperature, this method can effectively achieve higher Al doping concentrations.

[0046] Example 3 This embodiment aims to explore the effect of extending the synthesis time at a slightly lower main reaction zone temperature on powder quality and doping uniformity.

[0047] S1: System Assembly and Loading: This step is the same as in Example 1.

[0048] S2: Vacuuming and Atmosphere Control: This step is basically the same as in Example 1, except that high-purity argon gas is introduced to an absolute pressure of 100-120 mbar. A slightly higher pressure helps to further suppress excessive volatilization of the raw materials.

[0049] S3: Dual-coil heating and synthesis: This step is basically the same as in Example 1, except for the adjustment of process parameters: the power of the first group (upper) coil is set to 8800 W (corresponding to an upper zone temperature of approximately 2400 ℃), and the power of the second group (lower) coil is set to 950 W (corresponding to a lower zone temperature of approximately 1500 ℃). The heat preservation time is extended to 7 hours.

[0050] S4: Cooling and Product Collection: This step is the same as in Example 1.

[0051] The average aluminum doping concentration of the powder obtained in this embodiment was tested to be 1.8 × 10⁻⁶. 18 cm -3 Although the doping concentration was slightly lower than in Example 1, XRD full width at half maximum (FWHM) data showed superior crystal quality. This condition is suitable for scenarios with higher requirements for powder crystal quality and doping uniformity.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 is that: instead of using a double crucible and double coil system, 15g of Al4C3 powder was directly physically mixed with Si powder and C powder, and then placed together in a single crucible and heated for 5.5 hours with a single coil at a power of 9000 W.

[0053] Results: Analysis of the obtained powder showed that the aluminum doping concentration was extremely uneven, with the concentration at the head (simulated region near the seed crystal position) reaching 1×10⁻⁶. 18 cm -3 The tail concentration has dropped to 5×10 17 cm -3 The presence of unreacted carbon and aluminum compounds in the powder indicates premature depletion of the aluminum source.

[0054] Comparative Example 2 The difference between this comparative example and Example 1 is that the second (lower) coil is turned off, that is, the lower crucible is not heated separately, and the lower crucible is heated only by the heat from the upper crucible through heat conduction and radiation.

[0055] Results: Due to the actual crucible temperature being far below the temperature required for effective sublimation of Al4C3 (estimated <900 ℃), the aluminum source supply was severely insufficient. The average aluminum doping concentration of the resulting powder was only 3 × 10⁻⁶. 17 cm -3 High concentrations of p-type doping cannot be achieved.

[0056] Comparative Example 3 This comparative example aims to illustrate the necessity of porous graphite sheets in the powder synthesis process. The only difference between this comparative example and Example 1 is that: instead of placing porous graphite sheets at the bottom of the upper crucible, hollow graphite channels are directly connected to the upper crucible (similar to the traditional double crucible structure for crystal growth), the mixture of Si powder and C powder is directly piled at the bottom of the upper crucible (including the channel opening).

[0057] Results: During the heating process, as the Si powder melted at approximately 1414 °C, a large amount of liquid silicon flowed into the hollow connecting pipe under gravity and dripped into the lower crucible. Upon inspection after the reaction, it was found that: 1) the connecting pipe was severely blocked by solidified silicon, obstructing the aluminum vapor transport channel; 2) the Al4C3 surface in the lower crucible was covered with a layer of silicon, preventing effective sublimation of the aluminum source. The final collected powder had a low Al doping concentration (< 1×10⁻⁶). 17 cm -3 Furthermore, due to the loss of some Si, a large amount of unreacted carbon residue remains in the powder, resulting in extremely poor synthesis quality.

[0058] The above embodiments and comparative examples show that the porous graphite sheet with specific pore parameters (such as a porosity of 50% and a pore size of 40 μm) used in this invention, combined with a double crucible structure and independent temperature control by dual coils, is the key to achieving high-concentration, uniform Al-doped p-type SiC powder.

[0059] like Figure 2 As shown, under the steady-state temperature field provided in Example 1, the temperature inside the upper crucible is maintained at 2300-2500 ℃. This high-temperature environment ensures complete melting of the silicon powder and efficient solid-liquid-gas phase reaction with the carbon powder. The temperature field of the lower crucible is independently controlled at 1500-1800 ℃, which avoids premature decomposition of Al4C3 and achieves stable and long-term release of aluminum vapor. This solves the problem of uneven doping and low doping concentration caused by premature depletion of the aluminum source in the traditional p-type SiC powder synthesis process.

[0060] like Figure 3 As shown, in the graphite pipe under steady-state conditions provided in Example 1, the aluminum vapor velocity distribution ranges from 0.06 to 0.08 m / s.

[0061] like Figure 5 As shown, the Al-doped p-type α-SiC powder block provided in Example 1 is black.

[0062] like Figure 6 As shown, the Al-doped p-type α-SiC powder obtained after crushing in Example 1 is black.

[0063] like Figure 7As shown in the figure, the XRD pattern of the p-type α-SiC powder provided in Example 1 shows that its phases are 4H-SiC and 6H-SiC.

[0064] like Figure 8 As shown, the GDMS detection results of the p-type α-SiC powder provided in Example 1 show that the mass fraction of Al atoms in the p-type α-SiC powder provided in Example 1 is 0.22 wt% (corresponding to a doping concentration of approximately 1.58 × 10⁻⁶). 20 cm -3 ).

[0065] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0066] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing Al-doped p-type silicon carbide powder, characterized in that, include: The Al-doped p-type α-SiC powder synthesis device was placed in an induction heating furnace, sealed, evacuated, and filled with argon until the pressure inside the furnace reached 20~100 mbar. The first chamber is heated to 2300-2500℃ by the first heating element, so that the carbon powder and silicon powder react to form silicon carbide. The second chamber is heated to 1500-1800℃ by the second heating element and kept at that temperature for 4-8 hours, so that the aluminum source enters the first addition device in the form of aluminum vapor through the central control pipe and is incorporated into SiC to obtain Al-doped p-type α-SiC powder. The Al-doped p-type α-SiC powder synthesis apparatus includes: The first heating device includes a first cavity and a first heating element surrounding the first cavity. A porous graphite sheet is placed at the bottom of the first cavity, and carbon powder and silicon powder are placed on the porous graphite sheet. A hollow pipe, which is connected to the bottom of the first cavity; The second heating device has its top connected to the bottom of the hollow pipe. The second heating device includes a second cavity and a second heating element surrounding the second cavity. An aluminum source is placed at the bottom of the second cavity.

2. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The porous graphite sheet has a porosity of 40-60% and an average pore size of 20-60 μm.

3. The apparatus for synthesizing Al-doped p-type α-SiC powder according to claim 1, characterized in that, The first heating element is a first high-frequency induction coil, and the power of the first high-frequency induction coil is set to 8000-10000 W.

4. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The second heating element is a second high-frequency induction coil, and the power of the second high-frequency induction coil is set to 500-1500 W.

5. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The flow rate of the aluminum vapor is 0.06-0.08 m / s.

6. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The heat preservation process for the first and second cavities lasts for 4-8 hours.

7. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The first cavity includes an upper isostatic graphite crucible and a sealed furnace cover located on the graphite crucible, the second cavity is a lower isostatic graphite crucible, and the hollow pipe is a hollow graphite pipe.

8. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, Carbon fiber insulation felt is wrapped between the first cavity and the first heating element, between the second cavity and the second heating element, and on the outside of the hollow pipe.

9. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The aluminum source is Al4C3.

10. The method for preparing Al-doped p-type silicon carbide powder according to claim 1, characterized in that, The length of the hollow pipe is 150-180 mm.

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